1993 115 Johnson. Can't make this one out.

[James R]

This recently rebuilt and tested motor was out for a week and the boat sank, in shallow fresh water. Flushed the motor and no sign of sand or other crud. Stripped and cleaned the carbs. Replaced starter motor and solenoid. Flushed the fuel lines using my test fuel tank which is clean. Ran for while using my clean tank then started idling rough. Checked the sparks. All good. Stripped carbs and cleaned again. Found crud in the #4 idle jet. Replaced the inline filter and flushed the fuel line again. Fired her up and still running rough on idle. Watched all the sparks with my timing light. All good, no misses. Tried tapping the primer button every few seconds and the rough idle went away. Rough idle came back when I stopped using the primer button. Conclusion, running lean at idle. How can this be the carbs as they are spotless.
Any thoughts would be most welcome.

 

[Chris1956]

Re: 1993 115 Johnson. Can't make this one out.

Sounds like more crud in idle jets. Did you adjust the idle mixture properly? Did you adjust the carb floats to spec? Is timing correct?

 

[emdsapmgr]

Re: 1993 115 Johnson. Can't make this one out.

Agree. The idle passages in these carbs are pretty small. Does not take much to restrict them just enough to cause a rough idle or a lean sneeze at idle. You could use a spray bottle of boat gas (with oil) to test. Spray into each carb throat when running. When the idle improves, that may be the carb throat/cylinder with the fuel restriction.

 

[James R]

Re: 1993 115 Johnson. Can't make this one out.

Thanks guys. No adjustments on these carbs but I will try to isolate which carb or side of carb. Will let you know.

 

[James R]

Re: 1993 115 Johnson. Can't make this one out.

Isolated the cylinder to #4 using a spray bottle of 50:1. Stripped the carb including the welch plug. Nothing visual but I probed all the portings and jets and used a pressure can of carb cleaner. Reassembled and refitted. Motor ran normally. Each cylinder choked when the spray was used. No longer a lean on the #4.
When I service a motor I always use my fuel and tank. Just as well in this case. I spotted the recently fitted inline water trap filter with tape on the fittings. Spoke with the owner and he said it was Teflon tape. Duuuh. Explained that teflon tape is a no no.
Thanks for your help guys. Much appreciated.